Metal halogen electrochemical cell system

ABSTRACT

A metal halogen electrochemical energy cell system that generates an electrical potential. One embodiment of the system includes at least one cell including at least one positive electrode and at least one negative electrode, at least one electrolyte, a mixing venturi that mixes the electrolyte with a halogen reactant, and a circulation pump that conveys the electrolyte mixed with the halogen reactant through the positive electrode and across the metal electrode. Preferably, the positive electrode comprises porous carbonaceous material, the negative electrode comprises zinc, the metal comprises zinc, the halogen comprises chlorine, the electrolyte comprises an aqueous zinc-chloride electrolyte, and the halogen reactant comprises a chlorine reactant. Also, variations of the system and a method of operation for the systems.

The present application is a National Stage of PCT/US2008/051111, filedJan. 16, 2008, which is a continuation of U.S. application Ser. No.11/654,380, filed Jan. 16, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to metal halogen electrochemical energysystems.

2. Related Art

One type of electrochemical energy system uses a halogen component forreduction at a normally positive electrode, and an oxidizable metaladapted to become oxidized at a normally negative electrode during thenormal dispatch of the electrochemical system. An aqueous electrolyte isused to replenish the supply of halogen component as it becomes reducedat the positive electrode. The electrolyte contains the dissolved ionsof the oxidized metal and reduced halogen and is circulated between theelectrode area and a reservoir area and an elemental halogen injectionand mixing area, to be consumed at the positive electrode. One exampleof such a system uses zinc and chlorine system.

Such electrochemical energy systems are described in prior patentsincluding U.S. Pat. Nos. 3,713,888, 3,993,502, 4,001,036, 4,072,540,4,146,680, and 4,414,292. Such systems are also described in EPRI ReportEM-1051 (Parts 1-3) dated April 1979, published by the Electric PowerResearch Institute. The specific teachings of the aforementioned citedreferences are incorporated herein by reference.

SUMMARY OF THE INVENTION

There are certain weaknesses or disadvantages in prior electrochemicalenergy systems for standby applications. These include, but are notlimited to, the following:

-   -   an inability to store sufficient energy without requirement to        charge the system, precluding availability while in a discharged        condition;    -   complexity and inefficiency of requiring active cooling systems        during discharge, which can further reduce capacity;    -   ambiguities in diagnosing symptoms of failure, which can        significantly increase a probability of failure; and    -   hydrogen generation, which can be a significant and costly        safety issue.

Specific weaknesses or disadvantages in prior metal halogen systems forstandby applications also include, but are not limited to, thefollowing:

-   -   inability to maintain a state of readiness without significant        capacity loss due to self-discharge;    -   mal-distribution of zinc metal from internal shunt currents        between cells of differing potential further reduces available        capacity;    -   a long length of small diameter channels required for minimizing        shunt currents during operation further reduce system capacity        due to pumping losses;    -   metallic dendritic growth during the charge mode can permanently        damage a metal halogen system and lead to premature and        hazardous failure conditions.

The invention attempts to address some or all of these weaknesses anddisadvantages. The invention is not limited to embodiments that do, infact, address these weaknesses and disadvantages.

Some embodiments of the invention that attempts to address some or allof these weaknesses and disadvantages are metal halogen electrochemicalenergy cell systems. These embodiments preferably include at least atleast one positive and at least one negative electrode, a reaction zonebetween the positive electrode and the negative electrode, at least oneelectrolyte that includes a metal and a halogen, and a circulation pumpthat conveys the electrolyte through the reaction zone, wherein theelectrolyte and a halogen reactant are mixed before, at, or after thepump. Preferably, the positive electrode is made of porous carbonaceousmaterial, the negative electrode is made of zinc, the metal includezinc, the halogen includes chlorine, the electrolyte includes an aqueouszinc-chloride electrolyte, and the halogen reactant includes a chlorinereactant. One effect of this arrangement is generation of an electricalpotential.

A preferred embodiment further includes a mixing venture that mixes theelectrolyte and the halogen reactant, as well as a metering valve orpositive displacement pump that controls flow of the halogen reactant tothe mixing venturi.

A flow of the electrolyte preferably undergoes concurrent first, second,and third order binary splits before being conveyed through the reactionzone, thereby providing a same flow resistance for different paths tothe reaction zone.

Preferred embodiments of the systems also include a reservoir from whichthe electrolyte is conveyed by the circulation pump to the cell and towhich the electrolyte returns from the cell, an upward-flowingelectrolyte return manifold to facilitate purging of gas from the cell,and a return pipe through which the electrolyte returns from the cell tothe reservoir.

The halogen reactant preferably is supplied from an external source andpreferably is supplied under pressure. In this context, “external”refers to external to the system. An enthalpy of expansion of thehalogen from the external source tends to act to cool the system.Alternatively, the halogen reactant can be supplied from a sourceinternal to the system.

The systems preferably include plural such cells, each of which ishorizontal and plural of which are stacked vertically in the system.Vertical steps in cell geometry tend to result in interruptedelectrolyte flow paths within each of the plural cells, therebyinterrupting shunt currents that otherwise would continue to occur afterelectrolyte flow stops.

The plural cells preferably include plural cell frames. The cell framescan be circular to facilitate insertion of the plural cells into apressure containment vessel. The preferred form of the cell frames eachinclude a feed manifold element, distribution channels, flow splittingnodes, spacer ledges, flow merging nodes, collection channels, and areturn manifold element. When cell frames having this form are stacked,these structures form additional structures within the system. Inparticular:

-   -   the feed manifold element in each of the plural cells frames        aligns with the feed manifold element in another of the cell        frames, thereby forming a feed manifold;    -   the distribution channels and the flow splitting nodes in each        of the cell frames align with the distribution channels and the        flow splitting nodes in another of the cell frames, thereby        forming a distribution zone;    -   the positive electrode for each cell sits above or below the        negative electrode for each cell on the spaces ledges of the        cell frames, thereby forming alternating layers of positive        electrodes and negative electrodes;    -   the flow merging nodes and the collection channels in each of        the plural cells frames align with the flow merging nodes and        the collection channels in another of the cell frames, thereby        forming a collection zone; and    -   the return manifold element in each of the cell frames aligns        with the return manifold element in another of the cell frames,        thereby forming a return manifold.

The cell frames can include bypass conduit elements for fluid flow andelectrical wires or cables and preferably provide a pass-through for aalignment and clamping element to align and to hold the cell framestogether.

The invention is not limited to systems with cells that include cellframes.

Whether or not cell frames are used, preferred embodiments of thesystems include a feed manifold and a distribution zone for theelectrolyte to the plural cells, and a collection zone and a returnmanifold for the electrolyte from the plural cells. The positiveelectrode and the negative electrode in each cell preferably arearranged to maintain contact with a pool of electrolyte in each cellwhen electrolyte flow stops and the feed manifold, distribution zone,collection zone, and return manifold drain.

In some embodiments, a balancing voltage can be applied to inhibitelectrochemical reactions and thereby maintain system availability whenthe system is in a standby or stasis mode. A blocking diode also can beapplied to output terminals of the system to inhibit reverse currentflow within the system.

The basic operation of preferred embodiment of the system is as follows:aqueous electrolyte is sucked up from a reservoir and through a mixingventuri where halogen such as elemental chlorine is metered into anelectrolyte. The halogen mixes with and dissolves into the electrolytewhile its latent heat of liquefaction also cools the mixture. The cooledand halogenated aqueous electrolyte passes through the pump and isdelivered to positive electrodes in a stack assembly. The positiveelectrodes preferably are made of porous carbonaceous material such asporous graphite-chlorine. The electrolyte passes through the positiveelectrodes, reducing the dissolved halogen. The halogen-ion richelectrolyte then passes by one or more a negative electrode preferablymade of a metal such as zinc, where electrode dissolution occurs. Thesereactions yield power from the electrode stack terminals andmetal-halogen is formed in the electrolyte by reaction of the metal andthe halogen.

The invention also encompasses processes performed by embodiments of themetal halogen electrochemical energy cell system according to theinvention, as well as other systems and processes.

This brief summary has been provided so that the nature of the inventionmay be understood quickly. Other objects, features, and advantages ofthe invention will become apparent from the description herein, from thedrawings, which show a preferred embodiment, and from the appendedclaims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a metal halogen electrochemical energy cell systemaccording to the invention.

FIG. 2 illustrates flow paths of an electrolyte through the cell platesof an embodiment of the system illustrated in FIG. 1.

FIG. 3 illustrates cell frames that can be used in the systemillustrated in FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION

Electrolyte Energy Cell System

FIG. 1 illustrates a metal halogen electrochemical energy cell systemaccording to the invention.

One embodiment of the invention that attempts to address some or all ofthese weaknesses and disadvantages is a metal halogen electrochemicalenergy cell system. This embodiment includes at least at least onepositive and at least one negative electrode, a reaction zone betweenthe positive electrode and the negative electrode, at least oneelectrolyte that includes a metal and a halogen, and a circulation pumpthat conveys the electrolyte through the reaction zone. The electrolyteand a halogen reactant can be mixed before, at, or after the pump, forexample using a mixing venture. Preferably, the positive electrode ismade of porous carbonaceous material, the negative electrode is made ofzinc, the metal include zinc, the halogen includes chlorine, theelectrolyte includes an aqueous zinc-chloride electrolyte, and thehalogen reactant includes a chlorine reactant. One effect of thisarrangement is generation of an electrical potential.

The basic operation of this embodiment is as follows: aqueouselectrolyte is sucked up from a reservoir and through a mixing venturiwhere halogen such as elemental chlorine is metered into an electrolyte.The halogen mixes with and dissolves into the electrolyte while itslatent heat of liquefaction also cools the mixture. The cooled andhalogenated aqueous electrolyte passes through the pump and is deliveredto positive electrodes in a stack assembly. The positive electrodespreferably are made of porous carbonaceous material such as porousgraphite-chlorine. The electrolyte passes through the positiveelectrodes, reducing the dissolved halogen. The halogen-ion richelectrolyte then passes by one or more a negative electrode preferablymade of a metal such as zinc, where electrode dissolution occurs. Thesereactions yield power from the electrode stack terminals andmetal-halogen is formed in the electrolyte by reaction of the metal andthe halogen.

FIG. 1 shows an electrochemical energy system housed in containmentvessel 11 designed to achieve the foregoing. The system in FIG. 2includes two basic parts: stack assembly 12 and reservoir 19, as shownin FIG. 1.

Stack assembly 12 is made up of a plurality of cells or cell assemblies13 that include at least one porous electrode and at least one metalelectrode. The cells preferably are stacked vertically. Pressurizedhalogen reactant is supplied via feed pipe 15 from a source external tothe system through metering valve 17 to mixing venturi 18. Circulationpump 16 circulates the electrolyte from reservoir 19 through mixingventuri 18, through stack assembly 12, and back to reservoir 19 througha return pipe. It should be noted that some halogen reactant could beleft in the electrolyte when it returns back to the reservoir from thecell.

In a preferred embodiment, the porous electrodes include carbonaceousmaterial, the metal includes zinc, the metal electrode includes zinc,the halogen includes chlorine, the electrolyte includes an aqueouszinc-chloride electrolyte, and the halogen reactant includes a chlorinereactant.

In a preferred embodiment, this arrangement results in cells that eachhas an electrical potential of two volts, giving a stack arrangementwith 21 cells a potential of 42 volts. An enthalpy of expansion of thehalogen from the external source preferably cools the system. Thus, astrong potential can be provided without generating excessive heat.

Electrolyte Flows

FIG. 2 illustrates flow paths of an electrolyte through the cell platesof an embodiment of the system illustrated in FIG. 1. In this figure,the electrolyte flow paths 28 are represented by arrows. These paths arefrom feed manifold 21, to distribution zone 22, through porouselectrodes 23, over metal electrodes 25, to collection zone 26, throughreturn manifold 27, and to return pipe 29.

In a preferred embodiment, membranes 24 on a bottom of metal electrodes25 screen the flows of electrolyte from contacting the metal electrodesbefore passing through the porous electrodes. These membranes preferablyare plastic membranes secured to bottoms of the metal electrodes withadhesive. Other types of membranes secured in other ways also can beused. Alternatively, the membranes could be omitted.

With the arrangement shown in FIG. 2, the porous electrode and the metalelectrode in each cell are arranged to maintain contact with a pool ofelectrolyte in each cell when electrolyte flow stops and the feedmanifold, distribution zone, collection zone, and return manifold drain.

Furthermore, the vertically stacked cells and the geometry of the cellsresult in flow paths of the electrolyte within each of the plural cellsthat tend to interrupt shunt currents that otherwise would occur whenelectrolyte flow stops. These shunt currents are not desired becausethey can lead to reactions between the plates that corrode the metalplates without generating any usable potential.

Before being conveyed through the porous electrode, the electrolytemixed with the halogen reactant preferably undergoes first, second, andthird order splits to provide a same flow resistance for different pathsto the porous electrode. Each split preferably divides the flow by two,although this need not be the case. FIG. 3 illustrates one possible celldesign that can achieve these splits.

Cell Frames

FIG. 3 illustrates a cell design that uses cell frames to achieve thestructures and flows shown in FIG. 2. These cell frames preferablyinclude feed manifold element 31, distribution channels 32, flowsplitting nodes 33, spacer ledge 35, flow merging nodes 36, collectionchannels 37, return manifold element 38, and bypass conduit elements 34.

When these cell frames are stacked vertically with the electrodes inplace, these elements combine to form the elements shown in FIG. 2 asfollows:

-   -   the feed manifold element in each of the plural cells frames        aligns with the feed manifold element in another of the cell        frames, thereby forming a feed manifold;    -   the distribution channels and the flow splitting nodes in each        of the cell frames align with the distribution channels and the        flow splitting nodes in another of the cell frames, thereby        forming a distribution zone;    -   the porous electrode for each cell sits above or below the metal        electrode for each cell on the spaces ledges of the cell frames,        thereby forming alternating layers of porous electrodes and        metal electrodes;    -   the flow merging nodes and the collection channels in each of        the plural cells frames align with the flow merging nodes and        the collection channels in another of the cell frames, thereby        forming a collection zone;    -   the return manifold element in each of the cell frames aligns        with the return manifold element in another of the cell frames,        thereby forming a return manifold; and    -   the bypass conduit elements in each of the cell frames align        with the bypass conduit elements in another of the cell frames,        thereby forming bypass conduits for fluid flow and/or electrical        wires or cables.

The cell frames preferably are circular to facilitate insertion of theplural cells into a pressure containment vessel such as vessel 11.

The cell frame based design facilitates low-loss electrolyte flow withuniform distribution, bipolar electrical design, ease of manufacture,internal bypass paths, and elements by which the operational stasis mode(described below) can be achieved. Innovations of the cell frameinclude, but are not limited to, the flow-splitting design in thedistribution zone that include first, second, and third order splits inthe flow channels to deliver eight feed channels per cell to thereaction zone. This design attempts to ensure that each outlet to thereaction zone passes through the same length of channels, the samenumber and radius of bends, with laminar flow throughout and uniformlaminar flow prior to each split. The design encourages division of flowvolume equally, independent of flow velocity, uniformity of viscosity,or uniformity of density in the electrolyte. These features have beenfound to be of particular importance when a mixture of gaseous andliquid phases is fed through the system.

Alternatively, the same types of structures and flows (i.e., those shownin FIG. 2) can be achieved without using cell frames.

Modes of Operation

The energy cell system according to the invention preferably Cell hasthree modes of operation: Off Mode, Power Mode, and Stasis Mode. Thesemodes are described below in the context of a zinc-chlorine system.However, the modes also can be implemented using other metal-halogensystems.

Off Mode is typically used for storage or transportation. During OffMode, the circulation pump is off. A small amount of elemental chlorinein the stack assembly is reduced and combined with zinc ions to formzinc-chloride. The stack terminals preferably are connected via ashorting resistor, yielding a stack potential of zero volts. A blockingdiode preferably is used to prevent reverse current flow through thesystem via any external voltage sources.

During Power Mode the electrolyte circulation pump is engaged. Thecatholyte (i.e., electrolyte) containing dissolved chlorine iscirculated through the stack assembly containing the zinc anode plates.Electrons are released as zinc ions are formed and captured as chlorineions are formed, preferably with an electrical potential of 2.02 voltsper cell, thereby creating electrical power from the terminals of thecollector plates preferably located at each end of the stack assembly.The demand for power from the system consumes chlorine and reducespressure within the reservoir, causing the metering valve to releasehigher-pressure chlorine into the mixing venturi. This design featureaids both in speeding the dissolving of chlorine gas into theelectrolyte, and uniformly cooling the electrolyte without risk offreezing at the injection point. The injection rate preferably isdetermined by the electrochemical reaction rates within the stackassembly. The metering valve and the circulation pump preferably providesufficient response speed to match rapidly changing instantaneous powerdemands. As the compressed chlorine is released into the system, itsenthalpy of expansion should absorb sufficient heat to maintain theenergy cell within thermal operating limits.

During Stasis or Standby Mode, there should be little or no electrolyteflow or chlorine injection. The availability of the system preferably ismaintained via a balancing voltage that is applied to maintain systemavailability. This balancing voltage tends to prevent self-discharge bymaintaining a precise electrical potential on the cell stack tocounteract the electrochemical reaction forces that can arise with thecirculation pump off. The particular design of the cell plates tends tointerrupt shunt currents that would otherwise flow through the feed andreturn manifolds, while maintaining cell-to-cell electrical continuitythrough the bipolar electrode plates.

While these are preferred modes of operation, the invention is notlimited to these modes or to the details of these modes. Rather, someembodiments might have some of these modes, none of these modes, ordifferent modes of operation.

Generality of Invention

This application should be read in the most general possible form. Thisincludes, without limitation, the following:

-   -   References to specific techniques include alternative and more        general techniques, especially when discussing aspects of the        invention, or how the invention might be made or used.    -   References to “preferred” techniques generally mean that the        inventor contemplates using those techniques, and thinks they        are best for the intended application. This does not exclude        other techniques for the invention, and does not mean that those        techniques are necessarily essential or would be preferred in        all circumstances.    -   References to contemplated causes and effects for some        implementations do not preclude other causes or effects that        might occur in other implementations.    -   References to reasons for using particular techniques do not        preclude other reasons or techniques, even if completely        contrary, where circumstances would indicate that the stated        reasons or techniques are not as applicable.

Furthermore, the invention is in no way limited to the specifics of anyparticular embodiments and examples disclosed herein. Many othervariations are possible which remain within the content, scope andspirit of the invention, and these variations would become clear tothose skilled in the art after perusal of this application.

1. A metal halogen electrochemical system, comprising: (A) a pressurecontainment vessel that contains: (a) a stack of cells, wherein eachcell comprises: at least one positive electrode; at least one negativeelectrode; and a reaction zone between the positive electrode and thenegative electrode; and (b) an electrolyte mixture comprising (i) atleast one aqueous electrolyte comprising a metal and a halogen and (ii)a pressurized halogen reactant; (c) a stack of cell frames supportingthe stack of cells; (d) a feed manifold opening and a return manifoldopening in each cell frame in the stack of cell frames; (e) a feedmanifold formed by aligned feed manifold openings in the stack of cellframes; (f) a return manifold formed by aligned return manifold openingsin the stack of cell frames; (g) a plurality of distribution channelslocated in each cell frame, wherein the distribution channels areconfigured to introduce the electrolyte mixture from the feed manifoldto the reaction zone of each cell, and from the reaction zone to thereturn manifold; and wherein an inlet of the electrolyte mixture to thereaction zone and an outlet of the electrolyte mixture from the reactionzone are each located at or above the bottom of the positive electrodewithin the reaction zone; and the stack of cell comprises a verticalstack of horizontally positioned cells; and (B) a circulation pump thatis configured to convey a flow of the electrolyte mixture through thereaction zone so that the halogen reactant is reduced at the positiveelectrode to form a halogen ion rich electrolyte mixture, which passesby the negative electrode.
 2. The system of claim 1, wherein thepositive electrode comprises a porous carbonaceous material.
 3. Thesystem of claim 1, wherein the negative electrode comprises zinc; themetal comprises zinc; the halogen comprises chlorine; the aqueouselectrolyte comprises a zinc chloride electrolyte, and the halogenreactant comprises a chlorine reactant.
 4. The system of claim 1,wherein the circulation pump is located in the pressure containmentvessel, and the halogen reactant is supplied from a source internal tothe system.
 5. The system of claim 1, wherein the vessel contains anelectrolyte storage reservoir below the stack of cells, and thecirculation pump is configured to convey the flow of the electrolytemixture from the reservoir to the stack of cells through the feedmanifold.
 6. The system of claim 1, wherein said distribution channelsare formed by splitting nodes, each splitting the flow of theelectrolyte mixture into two, so that each of said distribution channelshas the same length and the same number and radius of bends.
 7. Thesystem of claim 1, further wherein the return manifold comprises anupward flowing return manifold configured to collect the electrolytemixture from the cells of the stack; and the stack maintains acell-to-cell electrical continuity and does not maintain a cell-to-cellelectrolyte continuity when the flow of the electrolyte mixture stops.8. The system of claim 1, wherein each cell frame comprises a spacerledge which supports an electrode of a cell in the stack of cells. 9.The system of claim 1, wherein the positive electrode and the negativeelectrode are arranged to maintain contact with a pool of theelectrolyte when the flow of the electrolyte mixture stops.
 10. A methodof using a metal halogen electrochemical system, comprising: (A)providing a system comprising: (a) a pressure containment vessel thatcontains at least one cell, the at least one cell comprises: at leastone positive electrode; at least one negative electrode; and a reactionzone between the positive electrode and the negative electrode; (B)mixing (i) at least one aqueous electrolyte comprising aqueous zincchloride and (ii) a pressurized halogen reactant comprising liquidchlorine, by dissolving the liquid chlorine in the aqueous zinc chlorideelectrolyte to form an electrolyte mixture, and (C) delivering a flow ofthe electrolyte mixture to the positive electrode of the cell, reducingthe halogen reactant at the positive electrode to form a halogen ionrich electrolyte mixture, and passing the halogen ion rich electrolytemixture by the negative electrode.
 11. The method of claim 10, wherein:the positive electrode comprises a porous carbonaceous material so thatsaid delivered electrolyte mixture passes through said positiveelectrode; the negative electrode comprises zinc; and the metalcomprises zinc.
 12. The method of claim 10, wherein said delivering isprovided by a circulation pump located in the pressure containmentvessel.
 13. The method of claim 10, wherein the halogen reactant issupplied from a source internal to the system.
 14. The method of claim10, wherein: the pressure vessel contains an electrolyte storagereservoir below the at least one cell; the electrolyte mixture ismaintained in the reservoir in a pressurized state; and wherein thesystem further comprises an upward flowing return manifold; and themethod further comprises collecting the electrolyte mixture from the atleast one cell through said manifold.
 15. The method of claim 10,wherein: the at least one cell comprises a horizontally positioned cell;said horizontally positioned cell has an inlet of the electrolytemixture to the reaction zone and an outlet of the electrolyte mixturefrom the reaction zone that are each located at or above the bottom ofthe positive electrode within the reaction zone; the at least one cellis located in a vertical stack of horizontally positioned cells; each ofthe cells in the stack comprises a cell frame that comprisesdistribution channels having the same flow resistance and wherein saiddelivering comprises delivering the electrolyte mixture to the positiveelectrode through the distribution channels; and the stack maintains acell-to cell electrical continuity and does not maintain a cell-to cellelectrolyte continuity when the flow of the electrolyte mixture stops.16. The method of claim 10, wherein the positive electrode and thenegative electrode are arranged to maintain contact with a pool of theelectrolyte when the flow of the electrolyte mixture stops.
 17. Themethod of claim 10, further comprising applying a balancing voltage tothe at least one cell to prevent a self-discharge of the system when theflow of the electrolyte mixture stops.
 18. The method of claim 10,wherein the system has a first intake conduit for the electrolyte and asecond intake conduit for the halogen reactant, which is separate fromthe first intake conduit.
 19. A metal halogen electrochemical systemcomprising: (A) a pressure containment vessel that contains: (a) avertical stack of a plurality of horizontal cells, each of the pluralityof horizontal cells comprising: at least one positive electrode; atleast one negative electrode; and a reaction zone between the positiveelectrode and the negative electrode; and (b) an electrolyte mixturecomprising (i) at least one aqueous electrolyte comprising a metal and ahalogen and (ii) a pressurized halogen reactant; and (B) a circulationpump that is configured to convey a flow of the electrolyte mixturethrough the reaction zone of each of the cells of the stack.